My dad's sister was very young and unmarried when she became an aunt for the first time. To make things stylish and acceptable for her, we were asked to call her 'aunty' in angrezi instead of the usual atte.
Calling one's real aunt 'aunty' is one thing, but, I don't know since when there has been this alarming trend of calling all married women 'aunty'!
My first encounter with this trend dates back to lo..ng ago - to the only time when I worked in an 'office'. I was new and the errand boy (a 40-50 yr old certified idiot!) came to me and said. 'Aunty.. if you want anything, just let me know. I'll get it for you'. The boss chided him - told him that since I was unmarried, he should be calling me 'maydam' and not 'aunty'. Thanks to that episode, I wasn't alarmed when people - sometimes, older than me - started calling me 'aunty'/ 'anti'!
It is another story that the errand boy, Srinivas, refused to call someone much younger 'maydam' and came up with ' Shomu' .... the only time in life that I have ever had a nickname! Thankfully, only Srinivas has called me by that name!
Over time, I have grown inure to being called 'aunty'. The other day, though, I was quite taken aback when my kid's classmate's maa called me 'aunty'! Back home, I was quite relieved when the mirror told me that my hair hadn't suddenly turned grey!
Since I don't go about calling strangers 'aunty' (I manage with 'just a moment'/ 'excuse me', if I have to address strangers), I gave the form of address some thought.
And, before giving up, I have concluded that 'aunty' must be an informal way of saying 'ma'am'!